1. Field of the Invention
The present invention relates generally to high-density automated tape libraries, and in particular, but not exclusively, to a cartridge positioning system for automated tape libraries. More specifically, the present invention provides an improved system and method for automatically exchanging cartridges between high-density automated tape libraries.
2. Background of the Invention
An automated tape library is a self-contained unit that includes a plurality of magnetic tape cartridge storage locations (e.g., cells, slots) that are serviced by a robot mechanism. The robot mechanism retrieves a magnetic tape cartridge from its assigned magnetic tape cartridge storage location in the automated tape library, and loads the retrieved cartridge into a designated tape drive. The tape drive facilitates the reading and/or writing of data from and/or to the magnetic media on the surface(s) of the tape. When the tape drive is finished with the magnetic tape cartridge, the robot mechanism retrieves the cartridge from the tape drive and returns the cartridge to its assigned storage location in the automated tape library.
Automated tape libraries are typically enclosed by a housing to prevent users from interfering with, or being injured by, the robot mechanism. Typically, a cartridge access port is provided to allow users to enter and retrieve magnetic tape cartridges into and from the automated tape library. The cartridge access port provides an apparatus to receive a magnetic tape cartridge from a user and then present the cartridge to the robot mechanism for storage in an assigned magnetic tape cartridge storage location. The apparatus can reverse this operation to enable the robot mechanism to retrieve the tape from the assigned storage location and present it at the access port to the user.
The existing enterprise class data storage market requires high-density, high performance, highly scalable, highly reliable, available and readily serviceable automated tape library systems. An example of such an enterprise class automated tape library system is the Streamline™ SL8500 Modular Library System produced by Storage Technology Corporation of Louisville, Colo. Such modular library systems are composed of a plurality of juxtaposed automated tape cartridge libraries. A pass-through mechanism is provided to interconnect two juxtaposed automated tape cartridge libraries to enable a robot mechanism in one automated tape cartridge library to pass a selected tape cartridge to a robot mechanism in the second automated tape cartridge library without user intervention. This ability to automatically exchange magnetic tape cartridges between libraries provides a load balancing capability, whereby idle tape drives in an automated tape cartridge library are accessible by a robot mechanism located in an adjacent automated tape cartridge library via the pass-through mechanism.
However, in order to meet the stringent density, performance, scalability, reliability, availability and serviceability requirements imposed by the enterprise class data storage market, the automated exchange of tape cartridges between automated tape libraries needs to be accomplished without significantly compromising the cartridge density of one or both of the juxtaposed automated tape libraries involved. Also, any apparatus used for automated cartridge exchange needs to provide adequate redundancy to ensure that the stringent enterprise class data storage availability requirements are met. Furthermore, such an automated cartridge exchange apparatus needs to meet the stringent enterprise class data storage serviceability requirements, by enabling the service of faulty components of the exchange apparatus without having to take any additional component of one or both of the adjacent automated tape libraries off-line.
A significant problem with the existing automated tape cartridge exchange devices is that their components are not serviceable without taking one or both of the linked automated tape libraries off-line. Another significant problem with many of the existing automated tape cartridge exchange devices is that only one magnetic tape cartridge can be exchanged at a time, and certain host software may be required to control the operations of the exchange devices and the multiple automated tape libraries involved. In any event, these exchange devices do not provide adequate serviceability and redundancy to meet the enterprise class data storage requirements currently imposed. Other existing automated tape libraries include a pass-through mechanism that provides some serviceability, but does not provide a redundant tape cartridge data path. However, the serviceability of these automated tape libraries is limited significantly, because the pass-through mechanism can be accessed for service only from the top due to the close proximity of the libraries involved. Consequently, in order to service an existing pass-through mechanism, at least one of the adjacent tape libraries has to be shut down.
Notwithstanding the above-described limitations of the existing automated tape library systems and cartridge exchange devices, a more critical problem relates to the inability of the existing automated tape library systems and cartridge exchange devices to meet the stringent density requirements imposed by the enterprise class data storage market. In other words, since the existing cartridge exchange devices are interposed between adjacent tape libraries, the relatively large size and structure of these devices significantly affects the ability of designers to minimize the distance between the tape libraries, which in turn, significantly limits the overall cartridge density of the automated tape library system involved.
Therefore, it is desirable to have an improved system and method for automatically exchanging tape cartridges between automated tape libraries arranged in close proximity, which system and method provide redundancy, high serviceability, and increased cartridge density relative to the prior art approaches.